Non-impact recording methods in the form of ink jet printing, thermal transfer printing and dye diffusion thermal transfer printing are presently of considerable interest because they are all capable of achieving high print speeds while operating relatively quietly and readily may produce full color, highlight color and monochrome records. The present invention is directed to the supplying of different color inks to one or more scanning recording heads in an ink jet printing device. This flexibility will enable multiple mono-color printing and highlight color printing, in addition to process color printing switchable to high speed monocolor printing, as will be described.
In one form of the ink jet recording process, droplets of ink are selectively expelled from an ink filled channel onto a spaced recording substrate. This process is often referred to as drop-on-demand. Propulsion may be accomplished by any one of several known methods for imparting pressure increases to confined portions of the ink adjacent to the ejection orifice. Examples of such pressure inducing devices are piezoelectric elements, acoustic generators, magnetic compressors or thermal elements.
Thermal, drop-on-demand ink jet printing systems make use of a thermal energy pulse of predetermined profile to produce a vapor bubble in an ink filled channel for expelling ink droplets from the channel orifice. A thermal energy generator, usually a resistor, is located in the channel a predetermined distance from the orifice. A resistor is associated with each nozzle, and each is individually addressed with a current pulse to rapidly heat and vaporize the ink. As the bubble grows, the ink bulges from the orifice and is contained by the surface tension of the ink as a meniscus. When the thermal energy is no longer applied, the bubble begins to collapse, causing the ink still in the channel, between the orifice and the bubble, to move toward the collapsing bubble. The volumetric contraction of the ink at the orifice results in the separation of the bulging ink as a droplet. The acceleration of the ink out of the orifice while the bubble is still growing provides the momentum and velocity of the droplet in a substantially straight line direction towards a recording medium, such as a paper sheet. Simultaneously with the ejection, a negative pressure condition is created within the channel causing ink to be drawn from a supply source into the channel, for filling it by capillary action.
This method has gained rapidly in popularity because it is possible to fabricate the channels and their bubble forming heaters simply and inexpensively by photolithographic thin film electronics methods. Recording heads including a dense array of channels, each with its thermal driver, may readily be made to a high resolution of 300 spots (orifices), or more, per inch. An ink jet recording head mounted upon a scanning carriage for forward and back traversing of a recording sheet, and having an array of orifices arranged normal to the scan direction, may "write" a scan line of information of 50 spots in a swath 1/6 inch wide. Koumura et al in U.S. Pat. No. 4,528,576 disclose several ink jet printer configurations including multiple scanning recording heads. In one form, the marking heads, on a scanning carriage, are aligned in the paper feed direction to enable simultaneous multicolor printing of recording segments with colored inks of black, cyan, magenta and yellow (B, C, M, Y) as the heads are moved forward and back relative to the recording sheet. In another arrangement, there is disclosed several marking heads disposed side-by-side upon a scanning carriage for projecting recording segments of colored inks in sequential scanning carriage passes.
In U.S. Pat. No. 4,774,529 (Paranjpe et al), assigned to the same assignee as the instant application, there is disclosed another form of a scanning recording head for an ink jet printer which is convertible from a multicolor printing mode to a higher speed monochrome printing mode. Several recording heads, for marking with colored inks of black, cyan, magenta and yellow, are aligned side-by-side in the scanning direction. When it is desired to print with a single color, usually black, one of the replaceable head cartridges is repositioned from a first level to a second level, so as to enable "writing" of at least two lines of information during a single scanning pass. Two lines may be printed simultaneously, thereby increasing the printing speed twofold. The printer disclosed in that patent is convertible from a multicolor mode to a higher speed monochrome mode, but since it requires the physical vertical displacement of an ink cartridge, accurate alignment of the shifted ink cartridge, sufficient to prevent relative positioning errors between the displaced arrays, is difficult to accomplish.
Alternatively, it is well known, as shown in U.S. Pat. No. 4,492,966, to mark with a line printer having orifices which extend in a direction substantially normal to the receptor sheet transport direction. These marking devices usually include one or more stationary marking heads extending the full width of the recording sheet.
It is an object of the present invention to increase the flexibility of operation of an ink jet marking head by providing a multicolor ink delivery system thereto and source selection means therefor.
It is a further object of this invention to provide a plural marking head printing mechanism which is capable of marking with more than one colored ink per head.
It is yet another object of this invention to provide an array of recording heads mounted upon a scanning carriage which may be operated in either a multicolor mode or a high speed monochrome mode.